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Old May 11th 2009, 02:27 AM   #1
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Circuit problem

In Figure (1) the box represents the circuit of a d.c. motor running at a steady speed. The motor behaves as a source of e.m.f. E (opposing that of the 120V battery) and an internal resistance of 4ohms. these are parallel with a 240ohm resistor. a current of 5.5A is drawn from the 120V battery with negligible internal resistance.
i) calculate the current through the 4ohm resistor
ii) the e.m.f. E

In figure (2), the motor is not running. An extra resistor R is added to limit the current on starting. What is the resistance of R if the current is to be limited to 20A?
i'm confused about the e.m.f. in the opposite direction thing.
thanks
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Old May 12th 2009, 03:40 AM   #2
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Solved! Yay!
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